Spanish Prime Minister Mariano Rajoy has said he will do "whatever is needed" to prevent the vote from taking place.

The Constitutional Court had already suspended the law and decree calling for a referendum on secession while it considers the national government's claim that it is unconstitutional.

The pro-independence coalition governing Catalonia says the October 1 ballot will go ahead despite a ruling by Spain's Constitutional Court suspending the vote until judges can rule on its legality. Authorities have also filed criminal charges against Catalan leader Carles Puigdemont, among other officials, saying he was only authorized to call an election not a referendum.

In a survey by the Catalan Centre of Opinion Studies in July, 41.1 percent backed independence while 49.9 percent rejected it. In such case, the law will enter into force the next day after the referendum and remain in force for half a year, allowing for a new parliament to take over to draft the constitution of an independent Catalonia.

The economically powerful Catalonia has a thriving population of 7.5 million and accounts for a fifth of Spain's economic output.

Spain's economic troubles and a perception that the region pays more in taxes than it receives in investments from Madrid have helped push the secessionist movement. The following year the demonstration took the shape of a giant "V" for "vote", while in 2015 the march resembled a human arrow.